Aerogel materials have extremely low coefficients of thermal conductivity due to their extremely high porosity, making them excellent thermal insulators. Aerogels are made using a technique called supercritical drying where a gel is heated and pressurized until the liquid component of the gel is supercritical, where a liquid and a gas exist simultaneously, and then depressurized and/or cooled into a gaseous phase. By avoiding the boundary between liquid and gaseous phases in this way, the gel does not develop the high surface tension in its structure that it would experience in “typical” drying.
The aerogel structure is typically created in a chamber where the supercritical fluid diffuses into the air in the chamber, and thus out of the gel. In some processes, the air in the chamber is then purged and replaced with new air is typically repeated several times until all or most of the liquid is gone from the gel, leaving an aerogel. However, such method requires a chamber that can be pressurized and heated and introduces some limitations such as size limitations of final aerogel product.